Leaders and workers from the sawmilling and textiles industries say companies have reduced their workers' hours and pay to prevent redundancies as business contracts.
The sectors employ a combined 30,000 people.
Sawmillers have been hit the hardest because of the plunging construction market, with building permits for new homes dropping by 28% last year.
The trend has taken hold as the Government prepares to open its Jobs Summit today in an effort to target key industries and get them through the global financial crisis.
Employers and unions seem agreed that changes to working hours may be a workable solution.
The Employers and Manufacturers Association said it was seeing an increase in the number of businesses asking for information about the four-day week.
"For those companies who need to make some changes in order to stay in business, there is a choice between downsizing and making a few people redundant or simply asking everybody to take a day off or making a few changes across the board so it only effects people a little bit," Northern Region employment services manager David Lowe said.
Andrew Little, of the country's biggest private sector union, the EPMU, said talk about the four-day working week had "now turned into the nine-day fortnight".
"I think there is a willingness to explore that and look at the potential costs for training," he said.
In some sectors, four-day weeks have been the forerunner of eventual closures.
The country's biggest spa pool maker, Leisureite, went down to a four-day, and then a three-day week, before going into liquidation last month.
Timber Industry Federation president Howard Tonge said domestic sales of sawn timber were now less than half those at the corresponding time last year.
The industry in New Zealand at present employs about 7000 people.
"Probably half of the industry is looking at working reduced hours. The examples are all overtime has gone, four-day weeks are common," he said.
"I've been involved since 1991 and I've never seen anything like this in terms of the speed with which the market contracted and the outlook going forward with no clear fix."
Textiles New Zealand director Paula Smith said the four-day week was also spreading through the clothing and textile industries.
"Some companies, if they know they haven't got any work on, have an agreement with their workers to work four days a week or have a week off or two weeks off because they haven't got any work," she said.
